Submitted to: Proceeding Symposium Native Plant Society of Texas
Publication Type: Proceedings
Publication Acceptance Date: 9/28/2007
Publication Date: 10/18/2007
Citation: Polley, H.W. 2007. Grasses and Gases: Impacts of Atmospheric CO2 Enrichment on Grasslands. In: Proceedings of the Native Plant Society of Texas, October 18-21, 2007, Georgetown, Texas. p. 24-27. Interpretive Summary: The concentration of carbon dioxide (CO2) gas in the atmosphere has increased by about 40% since the beginning of the Industrial revolution and is expected to reach at least double the pre-Industrial concentration within the century. CO2 enrichment typically increases plant growth, but the response of growth to CO2 differs among species. By preferentially stimulating growth of some species, CO2 enrichment may alter species abundances and contribute to vegetation change on grasslands. Scientists with the USDA-Agricultural Research Service in Temple, Texas used transparent, tunnel-shaped chambers to expose pasture plants and plants characteristic of tallgrass prairie to a gradient in CO2 spanning pre-Industrial to predicted concentrations. Objectives were to determine CO2 effects on grassland production and species composition. Enriching CO2 from pre-Industrial to elevated concentrations increased aboveground biomass of both pasture and prairie species, but also caused a shift in species abundances. CO2 enrichment increased aboveground biomass of perennial forb species (broad-leaf herbaceous plants) on pasture at the expense of biomass of the dominant grass. A similar trend of greater biomass of perennial forbs at higher CO2 was evident during the first year of CO2 treatment of prairie species growing on a deep clay soil. The continuing rise in atmospheric CO2 concentration likely is stimulating growth of grassland vegetation, but also may be favoring forb species at the expense of the perennial grasses that are the foundation of the livestock industry.
Technical Abstract: The concentration of carbon dioxide (CO2) gas in the atmosphere has increased by about 40% since the beginning of the Industrial revolution 200 years ago to the current level of 380 parts per million (ppm). Fossil fuel consumption and changes in land use account for much of this increase in CO2. Atmospheric CO2 concentration is increasing at the rate of about 1-3 ppm per year and is expected to reach at least double the pre-Industrial concentration within the century. Change in CO2 is nothing new. The CO2 concentration has increased and decreased through geological time, dropping to levels of 200 ppm or below during glacial periods including the last glaciation that ended about 15,000 ago. But, atmospheric CO2 now has reached levels that apparently are unprecedented from about ½ million years, and is increasing at a rate for which there is little or no precedent in Earth’s history.